1. Field of the Invention
The present invention relates to a process for converting an isoindoline pigment into an easily dispersible, brilliant, high-hiding to extremely high-hiding and weathering-fast pigmentary form.
2. Description of the Prior Art
Isoindoline pigments of the formula ##STR3## where A is ##STR4## or is the radical of a barbituric acid and B is the radical of a barbituric acid (for example the compound described in British Patent No. 1,187,667.
Example 76, and especially those in which both A and B are a barbituric acid radical, for example the compounds described in German Laid-Open Application DOS 2,041,999) are distinguished by good fastness characteristics. It is true that the pigments obtained by the methods of preparation described in the above publications are obtained in a finely particled form, but the pigments are agglomerated and harsh in texture so that the colorations obtained in surface coatings and plastics are specked, pale and dull and have low hiding power.
Using the customary methods of preparation of high-hiding organic pigments, such as heating the crude pigment in an organic solvent in the presence or absence of water (German Laid-Open Applications DOS Nos. 2,521,249, 2,302,508, 2,302,517, 2,302,482 and 2,521,249) or milling the pigment and then recrystallizing it from an organic solvent as described in German Laid-Open Application DOS No. 2,357,077, does not succeed, in the case of the above isoindoline compounds, in producing the desired pigmentary form.